Absorption: The ratio of how much a surface absorbs infrared radiation and later emits at a similar rate.

 

Active Emitter: Emits heat at a low to medium rate on its own, like people and pets.

 

Direct Emitter: Emits heat at a high rate on its own, like fire or the sun.

 

Distance to Spot Ratio: A measurement of the area from a specific distance. A 10:1 ratio indicates that the surface temperature measurement taken at 10 feet covers an area of 1 square foot.

 

Emissivity: An object's ability to emit heat.

 

Field of View (FOV): The total area, measured as an angle, within which a thermal imager views objects. The most common FOV for fire service TIs is about 50°. The FOV is much narrower than what we see with our eyes.

 

Hertz (Hz): A unit for measuring frequency. One Hertz equals one cycle per second. The higher the Hz, the better the refresh rate.

 

High Gain: Depending on the manufacturer, adjusting gain shifts the focus more toward heat. Images viewed in high gain can be more challenging to interpret.

 

Low Gain: The TI starts in low gain, where greyscales are visible through the device. This setting emphasizes life and layout details.

 

​

Mixed Gain: High and low gain are displayed on the same display. It works by changing the gain pixel by pixel, currently only on Seek TI.

​

NUC (Non-Uniformity Correction): This process corrects minor detector drift that occurs as the scene and environment change. It is normal to hear a click, and the image may freeze momentarily. Also called shuttering, this is when the frame freezes and resets.

 

Reflectivity: The amount of infrared radiation reflected by a surface, which is not related to the surface material itself.

 

Passive Emitter: An emitter that cannot generate heat on its own but can absorb and re-emit heat. Examples include a chair or a couch.

 

TI Basic: The mode in which the thermal imager starts when powered on, offering all features required by NFPA.

 

TI Basic Plus: An additional mode with extra features like zoom or hot and cold spot tracking.

 

Spot Temperature: The intersection of vertical and horizontal lines on the thermal imager display, indicating the approximate surface temperature of a specific area. It is typically shown in the lower right corner. Note that this provides an approximate temperature of a specific spot, not the entire image.

 

Transmissivity: The ability of a material to allow radiation to pass from one side to the other without being absorbed or reflected.